The present invention relates to a screw rotor tip design wherein the screw rotor tip has a geometry that allows the departure angle, pressure angle and lobe width to be selected or controlled independently of each other, thereby allowing greater flexibility in rotor design.
Screw compressors contain a variety of components that may directly affect the performance of the compressor. One of these components is the screw rotor tip. There are at least three parameters of the screw rotor tip that may add or detract from the performance or efficiency of the compressor. These parameters are the pressure angle, the lobe width and the departure angle. Although these parameters have various ranges in which their contribution to the compressor performance is minimized or maximized, certain elements of these parameters are constant.
FIG. 1 illustrates a conventional screw rotor tip having a tip portion 1, a short radius portion 2 and a transition 3 positioned therebetween.
The departure angle is shown at angle A and is defined as the angle between a line drawn tangent to tip 1 and a line drawn tangent through the surface of transition section 3 substantially adjacent to tip 1. As should be readily apparent, with this type of conventional tip structure, the departure angle A can be increased only by increasing the slope of transition section 3 which undesirably cuts down on the lobe width thickness 4 and which itself is undesirable, and which can also dictate a smaller radius for short radius portion 2 than is desired. Thus, in situations where a large departure angle A is desired, other features of the conventional lobe tip are adversely impacted.
Therefore, a need remains for a screw rotor tip design that allows the pressure angle, lobe width and departure angle to be determined and controlled independently of each other.
It is therefore the object of the present invention to provide a screw rotor tip design that has a departure angle, a pressure angle and a lobe width that can be determined and controlled independently.
Other objects and advantages will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages are readily attained.
According to the invention, a rotor for a screw rotor machine includes a shaft, and a plurality of lobes disposed on the shaft, each of the lobes extending radially outward from the shaft and having a tip surface, a rear surface and a transition section disposed between the tip surface and the rear surface, the transition section having an arcuate portion, a middle portion and a short radius portion, the arcuate portion being concave in shape so as to open away from the shaft and transition the tip surface into the middle portion.